This invention relates to an improved pliers and more specifically, to pliers which maintain cooperating jaws in a substantially parallel relationship when crossed handle members are moved to move the jaws from a closed position to an open position.
Tongue and groove pliers are often used to incrementally adjust a pivotal axis about which crossed handle members pivot, which members carry cooperating jaws to maintain an approximate parallel relation between the jaws when the jaws are opened to grasp an object. With this adjustable pivot, the jaws are held approximately parallel when the jaws are opened or closed. These tongue and groove pliers have a number of curved channels or grooves on one handle for receiving a tongue member carried by the other handle. The tongue can be manually and incrementally shifted from one channel to another to adjust the pivot point between the handles so as to obtain approximate parallel movement of the jaws when the jaws are being opened. Difficulties with using this type of pliers arises when a user must guess which channel to use for grasping a particular object.
To overcome the problem of incrementally shifting a tongue to a new groove, pliers have been developed using cams for incrementally adjusting the pivotal axis between the crossed members while a tool is being used to accommodate different sized objects grasped by the tool. U.S. Pat. No. 656,394 to Deiters & Bill; U.S. Pat. No. 163,642 to Dean; and U.S. Pat. No. 228,333 to Fawcett all illustrate the use of a cam to change the position of the pivotal axis as the jaws of the pliers are being opened or closed. In these devices, however, a pawl is used in cooperation with holes or teeth to incrementally lock the pivotal axis between the crossed members at predetermined points. Another patent, U.S. Pat. No. 3,685,097 to Scott, illustrates a clam opener tool having a variable pivot point joining a pair of plier members. The tool includes a slot receiving a pin and a first and second cam members which engage each other at a predetermined position to increase the mechanical advantage as the jaws are being closed. The first and second cam members are operative only when the jaws are being closed.
It is an object of the present invention to provide a pair of pliers where the jaws of the pliers are maintained substantially parallel when the pliers are manipulated from a closed position to an open position or vice versa. It is a further object of this invention to enable a user to fully manipulate this pair of pliers with one hand with the pivot point being changed continuously and automatically by cooperating cam members as the plier jaws are being open-ed or closed.